The partial combustion of a carbonaceous fuel with substantially pure oxygen yields synthesis gas consisting mainly of carbon monoxide and hydrogen. When the oxygen is supplied as an oxygen-containing gas, such as air or oxygen-enriched air, the synthesis gas formed also contains a substantial quantity of nitrogen. As used herein, the term carbonaceous fuel includes coals, such as brown coal, peat, wood, coke, soot, and the like, and liquid fuels, such as tar sand oil, shale oil, and mixtures of these liquid and particulate solid fuels.
Preferably, a moderator is also introduced into the reactor. The object of the moderator is to exercise a moderating effect on the temperature in the reactor. This is ensured by endothermic reaction between the moderator and the reactants and/or products of the synthesis gas preparation. Suitable moderators include steam and carbon dioxide.
The gasification is preferably carried out at a temperature in the range of from 1200.degree. to 1700.degree. C. nd at a pressure in the range of from 1 to 200 bar.
The reactor in which the preparation of synthesis gas takes place may have the shape of a sphere, a cone, a block or a cylinder. Preferably, the reactor has the shape of a cylinder.
The supply of carbonaceous fuel and oxygen-containing gas can take place through the bottom of the reactor. It is also possible to supply one of the reactants through the bottom of the reactor and one or more others through the side wall of the reactor. However, both the fuel and the oxygen-containing gas and the moderator are preferably supplied through the side wall of the reactor. This is advantageously performed by means of at least two burners arranged symmetrically in relation to the reactor axis in a lower part of the side wall.
Part of the slag is entrained by the synthesis gas as small droplets and leaves the reactor therewith. Although the gas outlet through which the synthesis gas is discharged may be arranged at or near the bottom of the reactor, it is preferably situated at or near the top. The remainder of the liquid slag formed in the combustion reaction drops down and is drained through the slag discharge located in the reactor bottom.
To remove the slag from the gasifying process, it is known to arrange a cooling or quenching water bath at the bottom of the gasifying vessel, in which water bath the slag, descending due to its weight, is captured and quenched, slag granules or agglomerates being formed. The slag granules are periodically or continuously removed from the water bath by means of conventional arrangements. The slag is suitably discharged through a slag outlet at the bottom of the water bath. When the gasification reactor and water bath are at pressures above 1 bar, a sluicing vessel is advantageously provided under the water bath.
Part of the slag which is solidified by cooling or quenching keeps floating on the water of the water bath. Occasionally, from 1 to 80% wt of the slag, discharged through the slag discharge of the reactor, keeps floating. When the floating slag forms a relatively thick layer, it can prevent molten slag from falling into the water bath. Accordingly, it is desirable to remove the floating slag from the water before the layer gets too thick.
When the floating slag is removed by drawing-off all the water from the water bath through the slag outlet at the bottom of the water bath, hot molten slag will contact the valve or valves in the slag outlet and cause considerable damage to the valve or valves. The present invention seeks to overcome this problem.